The present invention relates to a method of producing metallic structures on non-conductors by decomposing of metallo-organic compounds in a glow discharge with formation of a metallic film.
The production of metallic films on synthetic plastic materials is performed in a conventional manner normally in a wet chemical process. More particularly, the parts to be metallized are immersed in a special row of cleaning, etching, conditioning, activating and metallizing baths which are special for a substrate. The outer surfaces after the cleaning and conditioning are first seeded with prescious metal-containing solutions, and then metallized on the activated surfaces in accordance with a conventional process.
The treatment baths are as a rule aqueous solutions which however partially contain organic solvents. The disadvantage of this approach is partially high toxicity with considerable volatility of the utilized compounds, which requires respective safety precautions. In the case of polytetrafluorethylene because of the high hydrophoby of the material, only a purely organic formulation on the basis of sodium-carbanion complexes as etching solution is known, which insures a sufficient adhesion of the finally applied metal film. For the reason of the toxicity of the pretreatment chemistry and safety reasons polytetrafluorethylene as a substrate in the electronic industry cannot be used, despite the fact that with respect to its electrical and chemical characteristics it exceeds the majority of other materials. The discharge of the toxic treatment baths is also problematic.
A further essential disadvantage of the wet chemical process is that the relatively complicated treatment sequences are provided before the metallization for reaching the desired adhesion value. In each case the parameters of the process, such as for example temperature and treatment time must be maintained within narrow limits and therefore, in this condition a considerable process control is required. The danger of contamination of the treatment baths by the process-conditional fluctuations is high and can lead to substantial quality fluctuations. The aggressiveness of the treatment solutions in these conditions acts to reduce the quality of covering varnish or foil.
Another coating process includes a thermal dosing of volatile metal compounds. This process requires very high substrate temperatures (approximately 200.degree. C., and in practice between 300.degree. and 1,000.degree. C.). In the case of the above mentioned materials it can not be used or can be used with danger of damages to the material.